This invention relates to apparatus for in situ rejuvenation of asphalt pavement. More particularly this invention relates to a method and apparatus for mixing milled asphalt pavement and rejuvenating fluid in such rejuvenation.
Asphalt pavement consists essentially of an aggregate and sand mixture held together with a petroleum based binder, such as asphalt cement (ie. an xe2x80x9casphalt mixxe2x80x9d). With continued exposure to sun, moisture, traffic, freezing and thawing, asphalt mix surfaces degrade. The degradation is principally in the binder, rather than the aggregate and sand mixture which makes up the bulk of the asphalt mix. Also, much of the degradation occurs within the top two or three inches of the surface.
Traditionally, worn asphalt pavement was not restored but was instead torn up and replaced with new asphalt mix. This is a costly approach and creates a problem as to what to do with the torn up pavement. Accordingly, techniques and apparatus have been developed for restoring or rejuvenating the top few inches of an asphalt paved surface.
A typical road resurfacing machine has a heater for heating and softening the asphalt pavement surface as it passes along the surface. Following the heater is a xe2x80x9crakexe2x80x9d or xe2x80x9cscarifierxe2x80x9d which breaks up or xe2x80x9cscarifiesxe2x80x9d the softened pavement. The scarified pavement is generally crushed or xe2x80x9cmilledxe2x80x9d, blended with rejuvenating fluid and optionally additional sand or aggregate and redeposited. The redeposited material is spread out and rolled to create a rejuvenated surface comparable in quality to the original surface before degradation.
In order to produce a rejuvenated surface of high quality, it is important to ensure that an appropriate amount of rejuvenating fluid is added. Generally, a core sample or several core samples are initially taken of the surface to be rejuvenated and a desired ratio of rejuvenating material to milled material is analytically determined.
It is also important to thoroughly intermingle the milled material with the rejuvenating material, which will at least include a fluid but may also include additional sand and/or aggregate. In doing so it is important to maintain retention in the mixer while nevertheless maintaining volume throughput at a desired rate.
It is an object of the present invention to provide a method and apparatus for thoroughly blending the milled material with at least the rejuvenating fluid and with any other rejuvenating materials.
Improvements are provided in an asphalt pavement resurfacing machine having a transport structure, a heater mounted to the transport structure for heating an underlying asphalt pavement surface to form a heated surface, a mill mounted to the transport structure to follow the heater and grind the heated surface to form a milled material and to prepare the underlying surface to a preset depth, a rejuvenating fluid sprayer for introducing a rejuvenating fluid to the milled material and a mixer for blending the milled material with the rejuvenating fluid. According to the improvement, the mill is provided with at least two outlets of predetermined breadth. A respective height monitor is provided at each of the two outlets for determining the height of the milled material being discharged from each of the outlets. Respective forward facing inlets are provided into the mixer for receiving milled material from each outlet as the machine is advanced in a travel direction. A respective rejuvenating fluid sprayer is provided for spraying rejuvenating fluid on the milled material emanating from each outlet. The mixer may be a pug mill having a housing which has a downwardly facing bottom opening. The mixer may further have a plurality of paddles extending radially from a pug mill shaft mounted within the housing, rotatable with the shaft and orientated to blend the rejuvenating fluid with the milled material and to direct a blended material so formed toward at least one discharge outlet facing rearwardly relative to a travel direction of the resurfacing machine.
Windrow guides may be provided between the mill and the mixer to maintain windrow breadth and to guide the windrows into the mixer.
The improved machine may further comprise a control and processing station which receives input from each height monitor and from a resurfacing machine speed monitor to determine a discharge rate of milled material from each outlet and cause each sprayer to dispense rejuvenating fluid on the milled material at a desired rate based on the discharge rate.
A method is provided for asphalt paved road surface rejuvenation utilizing a structure having a heater, a mill and a mixer carried by a transport structure. The method comprises the steps of:
i) passing the heater over the road surface to heat and soften the road surface and form a preheated surface;
ii) passing the mill over the preheated surface and milling the preheated surface to loosen the preheated surface to a desired depth thus forming a milled material;
iii) discharging the milled material from opposite ends of the mill in respective windrows of known breadth;
iv) measuring windrow height and rate of advance of the transport structure;
v) comparing the breadth in step (iii) with the height and rate of advance in step (iv) to determine volume throughput;
vi) adding a rejuvenating fluid to each windrow at a dosage rate based on a desired weight percentage and the volume throughput;
vii) passing the mixer over the windrows and receiving the windrows through respective openings in the mixer;
viii) blending the rejuvenating fluid with the milled material in the mixer to form a blended mixture; and
ix) discharging the blended mixture from the mixer.
The mixer may be a pug mill extending transversely across the support structure and having sufficient breadth to capture the windrows simultaneously.
The pug mill may be operated in an inverted arrangement in which an open face thereof is adjacent the surface to utilize the surface as a bottom thereto.